The hallucinogenic brew Ayahuasca, a rich source of serotonergic agonists and reuptake
inhibitors, has been used for ages by Amazonian populations during religious ceremonies. Among all
perceptual changes induced by Ayahuasca, the most remarkable are vivid ‘‘seeings.’’ During such seeings,
users report potent imagery. Using functional magnetic resonance imaging during a closed-eyes
imagery task, we found that Ayahuasca produces a robust increase in the activation of several occipital,
temporal, and frontal areas. In the primary visual area, the effect was comparable in magnitude to
the activation levels of natural image with the eyes open. Importantly, this effect was specifically correlated
with the occurrence of individual perceptual changes measured by psychiatric scales. The activity
of cortical areas BA30 and BA37, known to be involved with episodic memory and the processing of
contextual associations, was also potentiated by Ayahuasca intake during imagery. Finally, we detected
a positive modulation by Ayahuasca of BA 10, a frontal area involved with intentional prospective
imagination, working memory and the processing of information from internal sources. Therefore, our
results indicate that Ayahuasca seeings stem from the activation of an extensive network generally
involved with vision, memory, and intention. By boosting the intensity of recalled images to the same
level of natural image, Ayahuasca lends a status of reality to inner experiences. It is therefore understandable
why Ayahuasca was culturally selected over many centuries by rain forest shamans to facilitate
mystical revelations of visual nature.